...FWIW: I've killed a bunch of ducks, mostly Sprig, Wigeon and Gadwall, some Brant and a honker this season so far with that Kent #5 Bismuth in 16 that I bought when on sale at Cabela's.

I also had a few boxes of Kent 1-1/16oz#5 TungstenMatrix left...

I'd say that when going out past, say, 40 yards, with MOD/FULL chokes, that the old Matrix kills them Dead In The Air better than does the Bismuth , so might be worth spending more on TM , especially if on a Special Hunt where maybe large Mallard might be the targeted species..
Have Fun, Good Luck!